1. Field of the Invention
This invention relates to printers which place a series of dots on underlying media to form a pattern, alpha numeric symbols, or a bar code. It relates more to those types of printers which are thermal printers wherein a print ribbon having a wax or other displaceable material thereon can be heated and disposed on an underlying media for printing thereon. Such underlying media can comprise paper, plastic, a web supporting a plurality of labels, or other media. The invention specifically relates to the print ribbon transport and drive control in a consistent manner to avoid various printing inconsistencies as well as an improved controller. Such printing inconsistencies can be light or dark print, improper alpha numeric symbols, or fuzzy printing as well as bar codes having either unclear or improper separations. This invention is in the field of the transport of the print ribbon, media, drive thereof, and control from a remote location.
2. Description of the Prior Art
The prior art of thermal printers relied upon various brakes, clutches, supports, and other apparatus in order to provide for the proper transport and drive of the print ribbon. The print ribbon has material thereon such as a wax or other type of heat sensitive material which can be used to imprint underlying media. The print ribbon has a very flexible and thin consistency. It borders on the fineness of a film like material of a flexible plastic sheet. Thus the print ribbon web should be maintained in a uniform and consistent position with respect to the web.
Disposed on the print ribbon is the print substance which must be disposed on underlying media. The substance of the print ribbon which is disposed under heated conditions is placed on the underlying media. It is placed at discrete points that must be accurately maintained. The accuracy is with regard to alpha numeric representations and particularly with regard to bar codes which have to be properly read.
During the process of displacement of the substance from the print ribbon, a heating element is used. The heating element can be an elongated bar having very discrete heating elements that conform to a certain number of dots per inch as desired. Such dots per inch in the way of heating elements can range up to six hundred dots per inch and more.
The print ribbon when passing under the heating element or printer head and on top of an underlying media and before and after is subject to wrinkling, striations, displacement, stretching, and other distortions. This is caused by tension, inertia, and other elements in the drive and transport systems and mechanism. In the past, it has been customary to compensate for these distortions with various clutches, controls, and supports. These mechanical elements which although workable in some cases did not always provide the best results. The distortions even after passing through the printer head are propagated backwardly to the printer head. Also, there was generally no way to compensate for this on a remote basis and/or as a real time function.
Further complicating this matter is the fact that the underlying media that is to be printed on must be driven over a platen which is a rotatable platen formed of a hard elastomeric material against which the print ribbon is guided and heated by the heating elements of the print head. Oftentimes, the print ribbons become mismatched with the underlying media, and distortions occur in a bar code which can be quite severe.
This invention utilizes a positive drive system for the print ribbon by a pair of D.C. brush motors that drive the take-up and supply spools. The motor velocities are measured by circuits that measure the Back EMF (BEMF) voltage of the motor drives. The movement and monitoring of the print ribbon can then be derived from the spool radius and the motor torque, as well as inertia and other dynamic aspects including the mass of the rolls on both the take-up and supply spools.
In order to maintain a print ribbon web without striations, stretched areas, or ridges and valleys, this invention incorporates a unique transport and drive system for the ribbon. This includes spring biased rollers in order to remove ribbon distortions. Also in order to balance the edges of the ribbon a gimbaled support that can be a roller is provided. Further to this extent, a remote control system is utilized to account for variables and corrections in the printing process.
An object of this invention is the control of the tension, movement and consistency of the print ribbon web. It is particularly important as it passes through the print head and over the underlying media that is to be printed.
A further enhancement is that the ribbon tension can be varied and maintained as to differently sized ribbon widths. The tension and movement is maintained on the print ribbon by means of rollers and a gimbaled or pivotal support. Also variable sized ribbons and media can be adjusted for automatically.
An object of this invention avoids prior art deficiencies by lessening print ribbon wrinkle. This is enhanced by rollers, and proper support across the width of the print ribbon web.
Another object of this invention is that it provides for tensioning and uniformity across the width of the print ribbon web. When prior art mechanical devices are used to maintain tension, especially friction type devices, another mechanism needs to be added to maintain the tension. This is usually a spring wrapped around a hub. This invention removes the need for this additional mechanism.
The invention provides rollers or other surfaces mounted on springs and/or gimbals or pivots which help to remove plastic ribbon set, striations, wrinkles, and inconsistencies from the ribbon. This is accomplished by working and guiding the ribbon in two different directions as it is taken off the feed spool, and balancing support across the width of the ribbon.
The support of the ribbon across its width is enhanced by a gimbaled or pivotal support that can be a plate, rod or roller. The center pivot of the gimbal can be adjusted by a motor or manually to accommodate various widths and edge dimensions of the print ribbon.
Finally, an automatic sensing and feedback system to control the printer is provided so that ongoing adjustments can be maintained to improve print quality and variably sized relationships.